Properly enqueue bootstrap into WordPress

function.php

<?php 
/**
 * Enqueue scripts and styles
 */
function electro_child_enqueue_scripts() {
    wp_enqueue_style( 'bootstrap', get_stylesheet_directory_uri() . '/css/bootstrap.css', array(), 20141119 );
}

add_action( 'wp_enqueue_scripts', 'electro_child_enqueue_scripts' );